std::isnan

From Cppreference

C++ Standard Library
Language Utilities library Strings library Containers library Algorithms library Iterators library Numerics library Input/output library Localizations library Regular expressions library (C++11) Atomic operations library (C++11) Thread support library (C++11)
Numerics library
Common mathematical functions
Functions Basic operations abs(int) labs llabs abs(float) fabs div ldiv fmod (C++11) remainder (C++11) remquo (C++11) fma (C++11) fmax (C++11) fmin (C++11) fdim (C++11) nan nanf nanl (C++11) (C++11) (C++11) Exponential functions exp exp2 (C++11) expm1 (C++11) log log10 log1p (C++11) ilogb (C++11) logb (C++11) Power functions sqrt cbrt (C++11) hypot (C++11) pow Trigonometric and hyperbolic functions sin cos tan asin acos atan atan2 sinh cosh tanh asinh (C++11) acosh (C++11) atanh (C++11) Error and gamma functions erf (C++11) erfc (C++11) lgamma (C++11) tgamma (C++11) Nearest integer floating point operations ceil floor round lround llround (C++11) (C++11) (C++11) trunc (C++11) nearbyint (C++11) rint lrint llrint (C++11) (C++11) (C++11) Floating point manipulation functions frexp ldexp scalbn scalbln (C++11) (C++11) modf nextafter nexttoward (C++11) (C++11) copysign (C++11) Classification fpclassify (C++11) isfinite (C++11) isinf (C++11) isnan (C++11) isnormal (C++11) signbit (C++11) Macro constants HUGE_VAL HUGE_VALF (C++11) HUGE_VALL (C++11) FP_INFINITE (C++11) FP_NAN (C++11) FP_NORMAL (C++11) FP_SUBNORMAL (C++11) FP_ZERO (C++11)

Defined in header <cmath>
int isnan( float arg );		(C++11 feature)
int isnan( double arg );		(C++11 feature)
int isnan( long double arg );		(C++11 feature)

Determines if the given floating point number arg is not-a-number (NaN).

[edit] Parameters

arg

-

floating point value

[edit] Return value

nonzero value if arg is NaN, ​0​ otherwise

[edit] See also

fpclassify (C++11)	categorizes the given floating point value (function)
isfinite (C++11)	checks if the given number has finite value (function)
isinf (C++11)	checks if the given number is infinite (function)
isnormal (C++11)	checks if the given number is normal (function)